The present invention pertains to the field of fluid shutoff valves. More particularly, the present invention pertains to valve seals that create seals between valve gates and valve housings.
Various types of fluid shutoff valves are utilized in numerous and different applications. While different styles of valves operate in different manners, each valve generally comprises a valve housing having a fluid passageway therethrough and a gate that moves relative to the housing in a manner such that the fluid passageway can be selectively and alternatively closed or opened. A butterfly valve, for example, typically comprises a circular or oval discoidal gate positioned within the fluid passageway of a valve housing at a location where the fluid passageway has a circular or oval cross-section. The gate of a butterfly valve is typically pivotal back and forth about a pivot axis that bisects the gate and that is oriented generally parallel to the opposite circular or oval faces of the discoidal gate. The pivot axis is also typically oriented perpendicular to fluid passageway in a manner bisecting the fluid passageway. The gate is typically dimensioned such that it is capable of completely or substantially blocking the fluid passageway when the gate is pivoted such that its opposite circular or oval faces are generally parallel or nearly parallel to the circular cross-section of the fluid passageway. The gate can be pivoted from this closed position to a fully opened position where its opposite circular or oval faces are oriented generally perpendicular to the circular cross-section of the fluid passageway. In such an opened position, the gate only minimally impedes fluid from flowing through the fluid passageway of the valve.
Some butterfly valves, such as large butterfly valves used for controlling the flow of water through dams, also comprise one or more valve seals configured to form a seal between the gate and the wall of the housing surrounding the gate when the gate is in the closed position. Each valve seal is typically partially positioned within an arcuate groove that extends radially outward into the housing wall from the fluid passageway. The valve seals can be formed of metal, rubber, polymeric material, or various other suitable materials. In some valves, the valve seals are substantially rigid and can be repositioned or adjusted in a manner to achieve the greatest congruency between the valve seals and the gate when the gate is in the closed position. In some valves, the valve seals may be resiliently deflectable in a manner such that they can resiliently deflect against the gate when the gate is in the closed position, and thereby maximize congruency.
Several design considerations influence the configuration of valve seals in butterfly valves. One such consideration is that very large pressure differentials across a gate of a butterfly valve may exist when the gate is in its closed position and the a valve seal must be able to maintain a seal between the housing and the gate while experiencing such pressure differentials. Additionally, when the gate of butterfly valve is in its opened position, high fluid flow rates through the valve may create pressure differentials between the fluid passageway and the grooves in which the valve seals are positioned. These pressure differentials act to draw the valve seals out of the grooves. As such, the valve seals must be firmly retained in the channels of the valve housing, even when not engaged with the gate.